1. Field of the Invention
The present invention relates to a method for manufacturing an olefinic thermoplastic elastomer composition having excellent tensile characteristics and molded appearance.
2. Description of the Related Art
Olefinic thermoplastic elastomers are widely used as energy-saving, resource-saving thermoplastic elastomers, particularly as substitutes for soft vinyl chloride and vulcanized rubber in automobile parts, industrial machine parts, electronic/electrical machine parts, construction materials, and the like because of being lightweight and easy to recycle.
Dynamic crosslinking methods are carried out in a variety of forms for kneading olefinic rubber and olefinic resin in the presence of a crosslinking agent. Among these, methods for admixing a polyolefin resin after dynamically heat-treating and crosslinking olefinic rubber together with a crosslinking agent in a Banbury mixer, and methods of dynamic crosslinking in the coexistence with polyolefin resin in a Banbury mixer are uneconomical in comparison with continuous methods because of the use of a batch-style Banbury mixer. In addition, the rubber and resin sometimes fail to disperse uniformly, and consistent quality is difficult to obtain.
A method in which olefinic rubber and olefinic resin are melted and mixed in advance in a Banbury mixer, the mixture is cooled and pelletized, and the resultant pellets are fed into an extruder along with a crosslinking agent and dynamically crosslinked inside the extruder has been proposed as a technique for obtaining an olefinic thermoplastic elastomer with stable quality and uniform dispersion of the rubber and resin, but this method is nonetheless lacking in economic feasibility in the sense that the rubber and the resin must be melted and mixed before being crosslinked.
Aimed at overcoming the foregoing drawbacks, a technique has been proposed, for example, in Japanese Patent Publication No. H2-52648, whereby an olefinic thermoplastic elastomer having excellent physical properties is continuously manufactured by a simplified method in which the rubber and resin are uniformly dispersed by using pelletized olefinic rubber and pelletized olefinic resin and by feeding these materials to a twin-screw extruder-together with a crosslinking agent.
In actuality however, the ethylene/α-olefin/polyene copolymer rubber mainly used as a raw material rubber for an olefinic thermoplastic elastomer is supplied in a block usually called a “bale”, and must therefore be fed to an extruder or other kneading machine and processed into pellets by way of a melted state to obtain a pelletized ethylene/α-olefin/polyene copolymer rubber, which in addition to being not necessarily economical, may also cause the temperature inside the extruder to reach high levels due to shear-induced heating, heat degradation to occur, and the performance of the final olefinic thermoplastic elastomer product to be adversely affected when ethylene/α-olefin/polyene copolymer rubber, which has a high molecular weight in comparison with a resin, is melted and kneaded alone under ordinary conditions.
An object of the present invention, which is aimed at overcoming the drawbacks that accompany conventional techniques such as those described above, is to provide a method whereby an olefinic thermoplastic elastomer composition having excellent tensile characteristics and molded appearance can be manufactured with high productivity.